As news broke on Sunday that Smith had been ruled out for the remainder of the second Ashes Test with delayed concussion, many felt it was proof he shouldn’t have been allowed to bat on during Australia’s first innings.

Steve Smith was felled by a nasty bouncer. (Photo by John Walton/PA Images via Getty Images)

Smith woke up on Sunday's fifth day with a headache and other symptoms, prompting Australia to replace him with Marnus Labuschagne - international cricket's first concussion substitute after the policy was introduced at the start of this series.

That Smith was allowed to resume his innings raised eyebrows, but CA's sports medicine manager Alex Kountouris noted about 30% of concussions did not present symptoms immediately.

"The reality is that only about one in five or one in six head impacts end up being concussions," he told reporters on Monday.

"So we just need to monitor them and we have a good protocol in place.

"If you look at that game, there was three other head impacts and only Steve developed a concussion.

"If we pulled out every player who had a head impact, we'd be pulling out 80 per cent of players who don't have a concussion. That would be an overreaction."

Kontouris said Australia's team doctor Richard Saw, who assessed Smith both on and off the field, was an expert in dealing with concussions and had the final say in whether players should return to play under CA's protocols.

The International Cricket Council has not sought to make it a requirement to have independent doctors in place, and Kontouris said CA was comfortable with the status quo.

Smith ‘didn’t seem to be all there’

“We build a protocol of concussion rules, which Smith passed so successfully he was back out in the middle half an hour after he had been a whisker from losing his life,” Know wrote on Sunday.

“Was he concussed? No, but he didn't seem to be all there either.

“He hoicked his second ball over midwicket like beach cricket, and then stood in front of a straight ball, walked off before the umpire had given his decision, and threw a review request over his shoulder. Huh? Wasn't this its own concussion test?”

There is no mandated minimum time on the sidelines beyond the initial 24 hours but Smith remains highly unlikely to recover in time for the third Test that starts in Leeds on Thursday.